Field of the Invention
The present invention relates to a battery measuring instrument and a measurement method, and more particular, to an apparatus for online measurement of a battery internal resistance and a measurement method of the apparatus for online measurement of the battery internal resistance.
Description of Related Art
Cell batteries with inherent characteristics of a low manufacturing cost, large capacity and low price have been widely applied in all science and technology areas in relation to the national economic development, including defense force, agriculture, and industrial areas and so on. Along with the continuous development and progress of science and technology, battery manufacturing companies continue to place higher requirements on the battery measuring instrument, which include the requirements for a higher precision of the testing parameters and reduced time in detecting all the parameters in addition to the comprehensive testing functions. An internal resistance of a battery is one of the significant parameters and technique index for judging the battery performance, and since the larger the capacity of the battery is, the smaller the internal resistance will be, the measurement of the internal resistance can be used to evaluate the size of the capacity, and moreover, a variation trend of the full life internal resistance value of the battery can be used to predict the lifespan of the battery. Therefore, the performance index i.e. the internal resistance of a battery attracts more and more attention, and the measurement of this index has important practical meaning.
The method of measuring the internal resistance of the battery currently adopted in this industry has two major types, including:
1. DC (direct current) discharge internal resistance measurement method: the DC discharge internal resistance measurement method is based on the physical formula R=U/I, a testing instrument forces a large constant DC current (at present, normally 40 A˜80 A large current) into the battery within a short duration (normally 2˜3 seconds), measures the voltage on two ends of the battery at the same time, and calculates the current internal resistance of the battery based on the formula. However, this measurement method has the following drawbacks: (1) this method is only applicable to measuring the large capacity battery or cell battery, and the small capacity battery cannot tolerate the 40 A˜80 A large current within 2˜3 seconds; (2) when the battery is loaded with the large current, the internal electrodes of the battery are polarized to produce a polarized internal resistance. Therefore, the measurement duration must be really short, or otherwise, the measurement error of the internal resistance value is significant; (3) the large current passes through the battery, causing damages to the internal electrodes of the battery and influencing the capacity and lifespan of the cell battery; (4) the measurement of the DC method can only be implemented in the static state or offline state, so the online measurement of the cell battery cannot be realized, which inevitably cause safety hazards to the equipment in operation.
2. AC (alternative current) buck internal resistance measurement method:
this AC method charges a constant AC current signal Is to a cell battery, measures a voltage response signal Vo on two ends of the cell battery and a phase difference cos, and determines the internal resistance R of the cell battery based on the impedance formula, but in the method, the internal resistance of the cell battery is small, the response voltage signal on two ends of the cell battery caused by the AC charging is weak and is prone to be interfered by the environmental noises, which is difficult to obtain the accurate measurement, and the AC current signal Is, the voltage response signal Vo, and the phase difference between the voltage and the current need to be measured. Therefore, this method is influenced by plenty of interference factors, which negatively impacts the precision, adds the complexity of the system, as well as influences the measurement precision.
Therefore, the battery measuring instrument in the prior art has the technical issues, which include in the online situation, the parameters available for detection are limited, the detected parameters are less precise, and the total time that the battery measuring instrument spend on detecting one battery is too long, which may be 3 S-5 S or more. Additionally, the battery measuring instrument in the prior art has the following defects: only couples of buttons are provided, which causes difficulties in operation; the display interface is complicated and difficult to understand; the testing result can only be obtained through observing the display screen. In view of the current status of the battery measuring instrument in the prior art, the battery measuring instrument and testing method encounter the technical difficulties/bottlenecks.